If I cover stuff you already know, please forgive me. There are bound to be other ways of doing these things and if somebody can point me to quicker and more efficient ways then I'd be grateful.
You should have had a root password from your host provider. With this you will be able to login to a shell. (Not sure about this? Easier from Linux, just type ssh yourdomain.tld into a console window; using windo$e, download PuTTY and install it, put in your server details and connect to port 22. Login with un root and pw whatever. I'm fairly sure you then ought to su to another user - could someone confirm this? I could be wrong).
Once you're in, you'll want to change the vhgost file for the relevant account.
cd /home/httpd/vhost/your.domain.tld/conf
vi vhost.conf
then do the necessary changes (to start inserting text in vi, hit the i key. When you're finished, press escape and do :wq enter).
If you need to alter apache config, go to
/etc/httpd/conf
vi httpd.conf.
Make sure you do a copy before you edit anything.
That ought to get you going.
Dale